Method for the decarbonizing of highly-carbonaceous ferrochromium



'LOUIS FRIDERICH, or GENEVA, swrrznn voELxLINeEN-oN-sAAn, GERMANY, A

1,608,270 PATENT OFFICE.

LANn'ANn WILHEL'M nonENnAUsnn, or ssIGNoRs ro srnmn snNn msxn, AK-

TIENGESELLSGHAFT, or SIEMENSSTADT, GERMANY, A 'oonromr oN or enn- IAN'Y.

METHOD eon THE nncAnBoNIzINe or nIenLY-oAnnoNAonoUs rnnnoennomum.

li'oDrawing. Application filed September 5, 1925 The present invention relates to improvements in methods for the decarbonizing of highly carbonaceous ferro-chroinium.

When producing ferro-chromium in elec- 6 trical furnaces a product is obtained which usually contains 8-10 per centcarbon. Such ferro-chromium is however .only available for fewptlrposes on account of its high content of carbon. In many branches of the-industry f. inst. in the high-grade steel industry for the producing of alloyed steel there is. now a'greatrdemand for ferro-chromium which is as much as possible free from carbon, viz, a ferro-chromium having a carbon COIltGIlllcbGlOW 1 per cent, or technically car-' bonless ferro-ch'roinium with a carbon con tent of 0,50,2 per cent.

These high grade ferro-chromiums'with a low content of carbon were hithereto pro- 0 ,duced in electric arc furnaces by melting .highly carbonaceous iferro-chromium (which had been obtained in the usual way) together with chromium ores, whereby the ferro-chromium was refined.' An exact contrql of this process is however not possible, wherefore the carbon content of the product obtained could not be fixed previously; Itwas therefore necessary in many cases to reeat the refining smeltings for several times :0 in order to reduce. the carbon content,sufficiently. This is also the cause for the extraordinary costs of the ferro-chromium poor in carbon in comparison with the costs of the usual product. I According to the present invention the process is not carried out.. in an arc furnace. but'in an induction furnace, whereby the permanent reducing effect of the electric are upon the charge-which hinders the refin- 40 ingis avoided. At the new method it will neither be necessary to cool the highly carbonaceous ferro-chromium obtained at the first stage of operation before delivering it y to the refining furnace and thereupon to "5 smelt it anew. On the contrary the process; 3 acdordin to the invention becomes fespe cially a yantageous and economical when carryingthe same through with \liquid. ferrochromium.

In its simplest form the invention consists in exposing the liquid charge tothe influ ence of the oxygen of the air at a suitable temperature and without using any refining Serial No. 54.793, and in Germany June 538, 1024. a

Scientific investigations have proved that I at this method the decarbonizing takes place 0 independently of the actual carbon contents of the charge and practically proportionally to the time used for the reaction; An .essential saving of time'is obtained in compari son to refining experiments performed with the best known slag coverings. At the prescut method it is also possible to analyze test" quantities at any stage of the process in'order to state the state of decarbonizing at any desired moment. A perpetual control 1 of the process is thus possible. Experiments have further shown that the method may be carried on with a'satisfactory result at any suitable 1' ing in the furnace. Hitherto the best results have been obtained by a -lining of chromite (chromic iron) and tar, because almost no wear occurs at this kind of lining. Another advantage lies in this, that the chromite simultaneously may be used as raw material for the producing of ferro-chrome. This simple form of the method may be perfectionated in different ways.

An acceleration and perfection of the refining process may' if. inst. I be obtained through increasing the oxygen contentsof .the air layer over the bath surface by conducting artificialoxygen to the same. Hereby simultanebusly the admission of nitrogen I is prevented.

The nitrogen which is taken up in smaller or greater quantities at the process may also be removed by known means such as t1ta-' mum, calclum, aluminium 'etc., a measure which also is appliable at other kinds-of posing, compounds such as super-oxidesto the bath or by refining by means of steam, whereby oxygen is created through the dissoc-iation which takes place on account of the high temperature at hand.

VVhat we claim as our invention'and desire to secure byLetters Patent is: The process of reducing low-carbon ferro chromium by re ning ferro-chromium rich in carbon, which comprises heating the charge in an induction furnace, keeping the said charge at a temperature at which neither the iron nor the chromium will oxi-- dize, ex osing the clean surface of the bathto the in uence of the air over the same,-and removing the nitrogen taken up dnring the process by addingto the chargea metal with great aflinity to nitrogen.

2. The process of producing ferro-chromium by refining ferro-chromium rich in carbon, which comprises heating the charge in an induction furnace, keeping the said charge at a temperature at which neither the iron nor the chromium will ox'idize,exposin g the clean surface of the bath to the influence of the air over the same,

and adding oxygen delivering easily decomand removing the nitrogen taken up during the process by adding to the charge a meta eat affinity to nitrogen.

e process of producing low-carbon ferro-chromium by re ning ferro-chromium rich in carbon, which comprises heating the charge in an induction furnace, keeping the with said charge at a temperature at which i neither the iron nor the chromium will oxidize, exposing the clean surface of the bath te, the influence of the air .over the same,

liais ng an' oxidizing gas to, the said air, and. p a in oxygen dellvering easily decomposing so id means such. as super oxides to the charge.

5.- The process" of roducing low-carbon ferro-chromium by re ning ferro-chromium rich in carbon, which comprises heating the charge in an induction furnace, keepi.

charge at a temperature at, which ne1ther' fthe iron' nor the chromium will oxidize, ex

posing the clean surface of the bath to the influence of the air above the same and lead-;

the

ing steam intothe'said air. v v 6. The process of roducing low-carbon ferro+chromium by re ing ferro-chromiu'm rich in. carbon, which comprises heating the low-carbon .whichfiheither the iron nor the chromium will oxidize, exposing the clean surface of the bath to the influence of the air above the same, leading steam into the said air,

and removing the nitrogen taken up during the process by adding to the charge a metal with great afiinity to nitro en.

7. The process ofproducing low-carbon ferro-chromi im by refining ferro-chromium rich inr'zarbon, which consists in heating a lining of chromite in an electric induction furnace, keeping the charge ata' temperature at which neither the iron nor the chromium will oxidize, exposing the clean sur-'- face of'the bath to the influence of the air above the same, and removing the nitrogen taken up during'the process by adding. to .the charge/a metal -withgreat afiinity to nitrogen. v

8. The process of producing low-carbon farm-chromium by refining ferro-chromium rich in carbon, which comprises heatin a lining of chromite in an electric induction furnace, keeping the charge at a temperature at whichne'ither the iron nor the chromium will oxidize, exposing the clean surface of. the bath to the influence of the air above the same, and adding oxygen delivering easily decomposing solid ,means such as super oxides to the charge.

9. The process ofroducing low-carbon ferro-chromium by re ning ferro-chromium rich in carbon, which comprlses heating a lining of chromite in an electric inductlo'n furnace, kee ing the charge ata' temperature at which neither the iron nor the chromium will oxidize, exposing the I clean surface of the bath to the influence of the air above the same, leading steam into the said air, and

wlth great afadding to the charge a metal finity tonitroge I v 10. The process of- "oducing low-carbon ferro-chromium by re ning ferro-chromium rich in-carbon, which' comprises heating'alining of chromite in an electric induction furnace, kee ing the charge at a'temperature at which neither theirqn norlthe chromium will oxidize, exposing the clean surface of the bath to the influence of the air above the same, leading into the said air, and.

removing the nitrogen absorbed during th process by addin oxygen delivering easily decomposing, soli substances such as super oxides to the charge.

11. The process of ferro-chr'omiumby re ning ferro-chromium rich in carbon, which com rises heating a f' lining of chromite in an. e ectric inductlon eous' medium.

furnace, to a temperature in the neighbor roducing low-carbon 12. The process of roducing low-carbon ferro-chromium by re ning ferro-chromium rich in carbon, which comprises heating a lining of chromite in an electric induction furnace, keeping the charge at a temperature in the neighborhood of 1425-1450 (3., exposing the clean surface of the bath to the influence of the air over the same, and removing the nitrogen taken up during the process-by adding to the charge a metal with great aflinity to nitrogen.

13. The process of producing low-carbon ferro-chromium by refining ferro-chromium rich in carbon, which comprises heating a lining of chromite in an electric induction furnace, keeping the charge at a temperature in the neighborhood of 14251450 0., exposing the clean surface of the bath to the influence of the air over the same, and adding oxygen delivering easily decomposing means such as super oxides to the charge;

14. The process tv roducing low-carbon ferro-chromium by re ning ferro-ch'romium rich in carbon, which comprises heating a lining of chromite in an induction furnace, keeping the charge at a temperature in the neighborhood of 1425-1450 C., exposing the clean surface of the bath to the influence of the air above the same and leading steam into the said air.

15. The process of producing low-carbon ferro-chromium b refining ferro-chromium rich in carbon, W ich comprises heating in an'electric induction furnace a lining of chro-' mite and a binding agent, keeping)the charge at a temperature .in the neigh orhood of 1425145O (3., exposing the clean surface of the bath to the influence of the air above the same, and removing the nitrogen taken up during -the process bhadding to. the

charge a metal with great a ity to nitro en.

16. Theprocess of roducing low-car on ferro-chromium by re ning ferro-chromium rich in carbon, which comprises heating a lining of'chromite in an electric induction furnace, a lining of chromite and a binding agent, keeping the charge at a temperature in the neighborhood of 1425-1450 0., exposing the clean surface of the bath to the influence of the air above the same, and addin oxygen delivering easily decomposing ,soli substances such as super oxides to the charge. 17. The process of roducing low-carbon ferro-chromium by re ning ferro-chromium rich in carbon, which comprises heating a lining of chromite and a binding agent in an, electric induction furnace, kee ing the charge at a temperature in the neig borhood of 1425445090., exposing the clean surface of the bath to the influence of the air above the same, and leading steam into the said air.

'In testimony whereof we afiix our signatures.

LOUIS FRIDERICH. WILHELM RODENHAUSER. 

